Sliding Wear Resistance of Metallic Coated Surface

The role of metallic coatings in sliding wear is examined experimentally. The results indicate that the tribological behavior of soft coatings is consistent with the delamination theory of wear, especially the critical nature of the plating thickness. It is shown that a reduction in wear rate of three orders of magnitude is possible when the coating material is softer than the substrate and thinner than a critical thickness. The optimum plate thickness is found to be of the order of 0.1 μm for cadmium, silver, gold or nickel plated on various types of steel. Cadmium, silver and nickel reduce wear only in non-oxidizing environments, whereas gold reduces wear both in air and in inert atmospheres.

The roughness of the substrate surface prior to plating and the nature of the coating/substrate bond have significant effects on the life of these coatings. The life of the coatings is increased by polishing the substrate to 0.1 μm (c.l.a.) prior to plating, and also by diffusion of the plated material into the substrate, which increases the coating/substrate bond strength.